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          LV05-03-线程同步-03-自旋锁
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            </details>

<h1 id="一、自旋锁的概念"><a href="#一、自旋锁的概念" class="headerlink" title="一、自旋锁的概念"></a><font size=3>一、自旋锁的概念</font></h1><h2 id="1-基本概念与特性"><a href="#1-基本概念与特性" class="headerlink" title="1. 基本概念与特性"></a><font size=3>1. 基本概念与特性</font></h2><p>自旋锁与互斥锁很相似，从本质上说也是一把锁，在访问共享资源之前对自旋锁进行上锁，在访问完成后释放自旋锁（解锁）；事实上，从实现方式上来说，互斥锁是基于自旋锁来实现的，所以自旋锁相较于互斥锁更加底层。</p>
<p>如果在获取自旋锁时，自旋锁处于未锁定状态，那么将立即获得锁（对自旋锁上锁）；如果在获取自旋锁时，自旋锁已经处于锁定状态了，那么获取锁操作将会在原地“自旋”，直到该自旋锁的持有者释放了锁。这与互斥锁很相似，都是为了保证共享资源在任意时间里，只有一个线程访问，这样就可以避免多线程导致共享数据错乱的问题。但是<strong>互斥锁在无法获取到锁时会让线程陷入阻塞等待状态</strong>；而<strong>自旋锁在无法获取到锁时，将会在原地“自旋”等待</strong>。“自旋”其实就是调用者一直在<strong>循环查看该自旋锁的持有者是否已经释放了锁</strong>，“自旋”一词因此得名。</p>
<p>自旋锁的不足之处在于：自旋锁一直占用的<code>CPU</code>，它在未获得锁的情况下，一直处于运行状态（自旋），所以占着<code>CPU</code>，如果不能在很短的时间内获取锁，这会使<code>CPU</code>效率降低。</p>
<h2 id="2-应用场景"><a href="#2-应用场景" class="headerlink" title="2. 应用场景"></a><font size=3>2. 应用场景</font></h2><p>自旋锁通常用于以下情况：需要保护的代码段执行时间很短，这样就会使得持有锁的线程会很快释放锁，而“自旋”等待的线程也只需等待很短的时间；在这种情况下就比较适合使用自旋锁，效率高！</p>
<h2 id="3-与互斥锁的比较"><a href="#3-与互斥锁的比较" class="headerlink" title="3. 与互斥锁的比较"></a><font size=3>3. 与互斥锁的比较</font></h2><ul>
<li>实现方式上的区别</li>
</ul>
<p>互斥锁是基于自旋锁而实现的，所以自旋锁相较于互斥锁更加底层；</p>
<ul>
<li>开销上的区别</li>
</ul>
<p>获取不到互斥锁会陷入阻塞状态（休眠），直到获取到锁时被唤醒；而获取不到自旋锁会在原地“自旋”，直到获取到锁；休眠与唤醒开销是很大的，所以互斥锁的开销要远高于自旋锁、自旋锁的效率远高于互斥锁；但如果长时间的“自旋”等待，会使得<code>CPU</code>使用效率降低，故自旋锁不适用于等待时间比较长的情况。</p>
<ul>
<li>使用场景的区别</li>
</ul>
<p>自旋锁在用户态应用程序中使用的比较少，通常在内核代码中使用比较多；因为自旋锁可以在中断服务函数中使用，而互斥锁则不行，在执行中断服务函数时要求不能休眠、不能被抢占（内核中使用自旋锁会自动禁止抢占），一旦休眠意味着执行中断服务函数时主动交出了<code>CPU</code>使用权，休眠结束时无法返回到中断服务函数中，这样就会导致死锁。</p>
<p>【注意事项】试图<strong>对同一自旋锁加锁两次必然会导致死锁</strong>，而试图对同一互斥锁加锁两次不一定会导致死锁，原因在于互斥锁有不同的类型，当设置为<code>PTHREAD_MUTEX_ERRORCHECK</code>类型时，会进行错误检查，第二次加锁会返回错误，所以不会进入死锁状态。</p>
<h1 id="二、基本操作"><a href="#二、基本操作" class="headerlink" title="二、基本操作"></a><font size=3>二、基本操作</font></h1><h2 id="1-自旋锁初始化"><a href="#1-自旋锁初始化" class="headerlink" title="1. 自旋锁初始化"></a><font size=3>1. 自旋锁初始化</font></h2><h3 id="1-1-pthread-spin-init"><a href="#1-1-pthread-spin-init" class="headerlink" title="1.1 pthread_spin_init() "></a><font size=3>1.1 pthread_spin_init() </font></h3><h4 id="1-1-1-函数说明"><a href="#1-1-1-函数说明" class="headerlink" title="1.1.1 函数说明"></a><font size=3>1.1.1 函数说明</font></h4><p>在<code>linux</code>下可以使用<code>man pthread_spin_init</code>命令查看该函数的帮助手册。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* Compile and link with -pthread. */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;pthread.h&gt;</span></span></span><br><span class="line"><span class="type">int</span> <span class="title function_">pthread_spin_init</span><span class="params">(<span class="type">pthread_spinlock_t</span> *lock, <span class="type">int</span> pshared)</span>;</span><br></pre></td></tr></table></figure>

<p><strong>【函数说明】</strong>该函数初始化一个自旋锁。</p>
<p><strong>【函数参数】</strong></p>
<ul>
<li><code>lock</code>：<code>pthread_spinlock_t *</code>类型，指向需要进行初始化操作的<strong>自旋锁对象</strong>。</li>
<li><code>pshared</code>：<code>int</code>类型，表示自旋锁的进程共享属性。</li>
</ul>
<details class="folding-tag" blue><summary> 点击查看 pshared 可以取的值 </summary>
              <div class='content'>
              <table>    <tr><td align="left" width=150px>PTHREAD_PROCESS_SHARED </td><td align="left">共享自旋锁。该自旋锁可以在多个进程中的线程之间共享</td></tr>    <tr><td align="left" width=150px>PTHREAD_PROCESS_PRIVATE</td><td align="left">私有自旋锁。只有本进程内的线程才能够使用该自旋锁</td></tr></table>
              </div>
            </details>

<p><strong>【返回值】</strong><code>int</code>类型，成功返回<code>0</code>；失败将返回一个非<code>0</code>的错误码。</p>
<p><strong>【使用格式】</strong>一般情况下基本使用格式如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需要包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;pthread.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 至少应该有的语句 */</span></span><br><span class="line"><span class="type">pthread_spinlock_t</span> spin;<span class="comment">/*定义自旋锁 */</span></span><br><span class="line">pthread_spin_init(&amp;spin, PTHREAD_PROCESS_PRIVATE);<span class="comment">/* 初始化自旋锁(私有) */</span></span><br></pre></td></tr></table></figure>

<p><strong>【注意事项】</strong><code>none</code></p>
<h4 id="1-1-2-使用实例"><a href="#1-1-2-使用实例" class="headerlink" title="1.1.2 使用实例"></a><font size=3>1.1.2 使用实例</font></h4><p>暂无。</p>
<h2 id="2-加锁和解锁"><a href="#2-加锁和解锁" class="headerlink" title="2. 加锁和解锁"></a><font size=3>2. 加锁和解锁</font></h2><h3 id="2-1-pthread-spin-lock"><a href="#2-1-pthread-spin-lock" class="headerlink" title="2.1 pthread_spin_lock() "></a><font size=3>2.1 pthread_spin_lock() </font></h3><h4 id="2-1-1-函数说明"><a href="#2-1-1-函数说明" class="headerlink" title="2.1.1 函数说明"></a><font size=3>2.1.1 函数说明</font></h4><p>在<code>linux</code>下可以使用<code>man pthread_spin_lock</code>命令查看该函数的帮助手册。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* Compile and link with -pthread. */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;pthread.h&gt;</span></span></span><br><span class="line"><span class="type">int</span> <span class="title function_">pthread_spin_lock</span><span class="params">(<span class="type">pthread_spinlock_t</span> *lock)</span>;</span><br></pre></td></tr></table></figure>

<p><strong>【函数说明】</strong>该函数将对自旋锁加锁，获取自旋锁。</p>
<p><strong>【函数参数】</strong></p>
<ul>
<li><code>lock</code>：<code>pthread_spinlock_t *</code>类型，指向已经初始化的<strong>自旋锁对象</strong>。</li>
</ul>
<p><strong>【返回值】</strong><code>int</code>类型，成功返回<code>0</code>；失败将返回一个非<code>0</code>的错误码。</p>
<p><strong>【使用格式】</strong>一般情况下基本使用格式如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需要包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;pthread.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 至少应该有的语句 */</span></span><br><span class="line"><span class="type">pthread_spinlock_t</span> spin;<span class="comment">/* 定义自旋锁 */</span></span><br><span class="line">pthread_spin_init(&amp;spin, PTHREAD_PROCESS_PRIVATE);<span class="comment">/* 初始化自旋锁(私有) */</span></span><br><span class="line"></span><br><span class="line">pthread_spin_lock(&amp;spin); <span class="comment">/*自旋锁上锁 */</span></span><br></pre></td></tr></table></figure>

<p><strong>【注意事项】</strong><code>none</code></p>
<h4 id="2-1-2-使用实例"><a href="#2-1-2-使用实例" class="headerlink" title="2.1.2 使用实例"></a><font size=3>2.1.2 使用实例</font></h4><p>暂无。</p>
<h3 id="2-2-pthread-spin-trylock"><a href="#2-2-pthread-spin-trylock" class="headerlink" title="2.2 pthread_spin_trylock() "></a><font size=3>2.2 pthread_spin_trylock() </font></h3><h4 id="2-2-1-函数说明"><a href="#2-2-1-函数说明" class="headerlink" title="2.2.1 函数说明"></a><font size=3>2.2.1 函数说明</font></h4><p>在<code>linux</code>下可以使用<code>man pthread_spin_trylock</code>命令查看该函数的帮助手册。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* Compile and link with -pthread. */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;pthread.h&gt;</span></span></span><br><span class="line"><span class="type">int</span> <span class="title function_">pthread_spin_trylock</span><span class="params">(<span class="type">pthread_spinlock_t</span> *lock)</span>;</span><br></pre></td></tr></table></figure>

<p><strong>【函数说明】</strong>该函数将对自旋锁加锁，获取自旋锁。类似于<code>pthread_spin_lock()</code>，不同之处在于，如果<code>lock</code>引用的自旋锁当前处于锁定状态，那么调用将立即返回错误<code>EBUSY</code>，而不是自旋。</p>
<p><strong>【函数参数】</strong></p>
<ul>
<li><code>lock</code>：<code>pthread_spinlock_t *</code>类型，指向已经初始化过的<strong>自旋锁对象</strong>。</li>
</ul>
<p><strong>【返回值】</strong><code>int</code>类型，成功返回<code>0</code>；失败将返回一个非<code>0</code>的错误码。</p>
<p><strong>【使用格式】</strong>一般情况下基本使用格式如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需要包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;pthread.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 至少应该有的语句 */</span></span><br><span class="line"><span class="type">pthread_spinlock_t</span> spin;<span class="comment">/*定义自旋锁 */</span></span><br><span class="line">pthread_spin_init(&amp;spin, PTHREAD_PROCESS_PRIVATE);<span class="comment">/* 初始化自旋锁(私有) */</span></span><br><span class="line"></span><br><span class="line">pthread_spin_trylock(&amp;spin); <span class="comment">/*自旋锁上锁 */</span></span><br></pre></td></tr></table></figure>

<p><strong>【注意事项】</strong><code>none</code></p>
<h4 id="2-2-2-使用实例"><a href="#2-2-2-使用实例" class="headerlink" title="2.2.2 使用实例"></a><font size=3>2.2.2 使用实例</font></h4><p>暂无。</p>
<h3 id="2-3-pthread-spin-unlock"><a href="#2-3-pthread-spin-unlock" class="headerlink" title="2.3 pthread_spin_unlock() "></a><font size=3>2.3 pthread_spin_unlock() </font></h3><h4 id="2-3-1-函数说明"><a href="#2-3-1-函数说明" class="headerlink" title="2.3.1 函数说明"></a><font size=3>2.3.1 函数说明</font></h4><p>在<code>linux</code>下可以使用<code>man pthread_spin_unlock</code>命令查看该函数的帮助手册。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* Compile and link with -pthread. */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;pthread.h&gt;</span></span></span><br><span class="line"><span class="type">int</span> <span class="title function_">pthread_spin_unlock</span><span class="params">(<span class="type">pthread_spinlock_t</span> *lock)</span>;</span><br></pre></td></tr></table></figure>

<p><strong>【函数说明】</strong>该函数用于对自旋锁解锁、释放自旋锁。</p>
<p><strong>【函数参数】</strong></p>
<ul>
<li><code>lock</code>：<code>pthread_spinlock_t *</code>类型，指向已经初始化过的<strong>自旋锁对象</strong>。</li>
</ul>
<p><strong>【返回值】</strong><code>int</code>类型，成功返回<code>0</code>；失败将返回一个非<code>0</code>的错误码。</p>
<p><strong>【使用格式】</strong>一般情况下基本使用格式如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需要包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;pthread.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 至少应该有的语句 */</span></span><br><span class="line"><span class="type">pthread_spinlock_t</span> spin;<span class="comment">/*定义自旋锁 */</span></span><br><span class="line">pthread_spin_init(&amp;spin, PTHREAD_PROCESS_PRIVATE);<span class="comment">/* 初始化自旋锁(私有) */</span></span><br><span class="line"></span><br><span class="line">pthread_spin_lock(&amp;spin); <span class="comment">/*自旋锁上锁 */</span></span><br><span class="line">pthread_spin_unlock(&amp;spin); <span class="comment">/* 自旋锁解锁 */</span></span><br></pre></td></tr></table></figure>

<p><strong>【注意事项】</strong><code>none</code></p>
<h4 id="2-3-2-使用实例"><a href="#2-3-2-使用实例" class="headerlink" title="2.3.2 使用实例"></a><font size=3>2.3.2 使用实例</font></h4><p>暂无。</p>
<h2 id="3-自旋锁销毁"><a href="#3-自旋锁销毁" class="headerlink" title="3. 自旋锁销毁"></a><font size=3>3. 自旋锁销毁</font></h2><h3 id="3-1-pthread-spin-destroy"><a href="#3-1-pthread-spin-destroy" class="headerlink" title="3.1 pthread_spin_destroy() "></a><font size=3>3.1 pthread_spin_destroy() </font></h3><h4 id="3-1-1-函数说明"><a href="#3-1-1-函数说明" class="headerlink" title="3.1.1 函数说明"></a><font size=3>3.1.1 函数说明</font></h4><p>在<code>linux</code>下可以使用<code>man pthread_spin_destroy</code>命令查看该函数的帮助手册。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* Compile and link with -pthread. */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;pthread.h&gt;</span></span></span><br><span class="line"><span class="type">int</span> <span class="title function_">pthread_spin_destroy</span><span class="params">(<span class="type">pthread_spinlock_t</span> *lock)</span>;</span><br></pre></td></tr></table></figure>

<p><strong>【函数说明】</strong>该函数销毁一个不再使用的自旋锁。</p>
<p><strong>【函数参数】</strong></p>
<ul>
<li><code>lock</code>：<code>pthread_spinlock_t *</code>类型，指向需要进行销毁的<strong>自旋锁对象</strong>。</li>
</ul>
<p><strong>【返回值】</strong><code>int</code>类型，成功返回<code>0</code>；失败将返回一个非<code>0</code>的错误码。</p>
<p><strong>【使用格式】</strong>一般情况下基本使用格式如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需要包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;pthread.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 至少应该有的语句 */</span></span><br><span class="line"><span class="type">pthread_spinlock_t</span> spin;<span class="comment">/*定义自旋锁 */</span></span><br><span class="line">pthread_spin_destroy(&amp;spin);<span class="comment">/* 销毁自旋锁 */</span> </span><br></pre></td></tr></table></figure>

<p><strong>【注意事项】</strong><code>none</code></p>
<h4 id="3-1-2-使用实例"><a href="#3-1-2-使用实例" class="headerlink" title="3.1.2 使用实例"></a><font size=3>3.1.2 使用实例</font></h4><p>暂无。</p>
<h2 id="4-自旋锁使用实例"><a href="#4-自旋锁使用实例" class="headerlink" title="4. 自旋锁使用实例"></a><font size=3>4. 自旋锁使用实例</font></h2><details class="folding-tag" blue><summary> 点击查看实例 </summary>
              <div class='content'>
              <figure class="highlight c"><figcaption><span>test.c</span></figcaption><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span>  <span class="comment">/* fopen fputc*/</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;pthread.h&gt;</span><span class="comment">/* pthread_create pthread_exit */</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;unistd.h&gt;</span> <span class="comment">/* sleep */</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;string.h&gt;</span> <span class="comment">/* strlen */</span></span></span><br><span class="line"></span><br><span class="line">FILE *fp;<span class="comment">/* 定义一个文件指针变量 */</span></span><br><span class="line"></span><br><span class="line"><span class="meta">#<span class="keyword">define</span> macro_spin 0 <span class="comment">/* 0,不使用自旋锁；1,使用自旋锁 */</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">if</span> macro_spin == 1</span></span><br><span class="line"><span class="type">pthread_spinlock_t</span> spin;<span class="comment">/* 定义自旋锁 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line"></span><br><span class="line"><span class="type">void</span> *<span class="title function_">threadMutex1</span><span class="params">(<span class="type">void</span> *arg)</span>;</span><br><span class="line"><span class="type">void</span> *<span class="title function_">threadMutex2</span><span class="params">(<span class="type">void</span> *arg)</span>;</span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc, <span class="type">char</span> *argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="type">int</span> ret;</span><br><span class="line">	<span class="type">pthread_t</span> tid1, tid2;</span><br><span class="line">	<span class="comment">/* 创建自旋锁(私有) */</span></span><br><span class="line"><span class="meta">#<span class="keyword">if</span> macro_spin == 1</span></span><br><span class="line">	pthread_spin_init(&amp;spin, PTHREAD_PROCESS_PRIVATE);</span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line">	<span class="comment">/* 1. 以追加读写的方式使用标准IO打开一个文件 */</span></span><br><span class="line">	fp = fopen(<span class="string">&quot;test.txt&quot;</span>, <span class="string">&quot;a+&quot;</span>);</span><br><span class="line">	<span class="comment">/* 2. 判断是否打开成功 */</span></span><br><span class="line">	<span class="keyword">if</span>(fp == <span class="literal">NULL</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		perror(<span class="string">&quot;open error&quot;</span>);</span><br><span class="line">		<span class="keyword">return</span> <span class="number">-1</span>;</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="comment">/* 3. 创建两个线程 */</span></span><br><span class="line">	ret = pthread_create(&amp;tid1, <span class="literal">NULL</span>, threadMutex1, <span class="literal">NULL</span>);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;This is threadMutex1 thread create,ret=%d,tid1=%lu\n&quot;</span>, ret, tid1);</span><br><span class="line">	ret = pthread_create(&amp;tid2, <span class="literal">NULL</span>, threadMutex2, <span class="literal">NULL</span>);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;This is threadMutex2 thread create,ret=%d,tid2=%lu\n&quot;</span>, ret, tid2);</span><br><span class="line">	<span class="comment">/* 4. 等待回收线程(设置线程分离) */</span></span><br><span class="line"></span><br><span class="line">	<span class="keyword">while</span>(<span class="number">1</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		sleep(<span class="number">1</span>);</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="type">void</span> *<span class="title function_">threadMutex1</span><span class="params">(<span class="type">void</span> *arg)</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="type">int</span> i = <span class="number">0</span>;</span><br><span class="line">	<span class="type">char</span> str[]=<span class="string">&quot;I write threadMutex1 line\n&quot;</span>;</span><br><span class="line">	<span class="comment">/* 设置线程分离，结束后自动回收 */</span></span><br><span class="line">	pthread_detach(pthread_self());</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;This is a threadMutex1 thread!\n&quot;</span>);</span><br><span class="line">	<span class="comment">/* 按字符将字符串写入文件 */</span></span><br><span class="line">	<span class="keyword">while</span>(<span class="number">1</span>)</span><br><span class="line">	&#123;</span><br><span class="line"><span class="meta">#<span class="keyword">if</span> macro_spin == 1</span></span><br><span class="line">		pthread_spin_lock(&amp;spin); <span class="comment">/* 自旋锁上锁 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line">		<span class="keyword">for</span>(i = <span class="number">0</span>; i&lt;<span class="built_in">strlen</span>(str); i++)</span><br><span class="line">		&#123;</span><br><span class="line">			fputc(str[i], fp);</span><br><span class="line">			usleep(<span class="number">100</span>);</span><br><span class="line">		&#125;</span><br><span class="line"><span class="meta">#<span class="keyword">if</span> macro_spin == 1</span></span><br><span class="line">		pthread_spin_unlock(&amp;spin); <span class="comment">/* 自旋锁解锁 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line">		usleep(<span class="number">1000</span>);</span><br><span class="line">	&#125;</span><br><span class="line">	pthread_exit(<span class="string">&quot;threadMutex1 exit!&quot;</span>);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="type">void</span> *<span class="title function_">threadMutex2</span><span class="params">(<span class="type">void</span> *arg)</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="type">int</span> i = <span class="number">0</span>;</span><br><span class="line">	<span class="type">char</span> str[]=<span class="string">&quot;I write threadMutex2 line\n&quot;</span>;</span><br><span class="line">	<span class="comment">/* 设置线程分离，结束后自动回收 */</span></span><br><span class="line">	pthread_detach(pthread_self());</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;This is a threadMutex2 test!\n&quot;</span>);</span><br><span class="line">	<span class="comment">/* 按字符将字符串写入文件 */</span></span><br><span class="line">	<span class="keyword">while</span>(<span class="number">1</span>)</span><br><span class="line">	&#123;</span><br><span class="line"><span class="meta">#<span class="keyword">if</span> macro_spin == 1</span></span><br><span class="line">		pthread_spin_lock(&amp;spin); <span class="comment">/* 自旋锁上锁 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line">		<span class="keyword">for</span>(i = <span class="number">0</span>; i&lt;<span class="built_in">strlen</span>(str); i++)</span><br><span class="line">		&#123;</span><br><span class="line">			fputc(str[i], fp);</span><br><span class="line">			usleep(<span class="number">100</span>);</span><br><span class="line">		&#125;</span><br><span class="line"><span class="meta">#<span class="keyword">if</span> macro_spin == 1</span></span><br><span class="line">		pthread_spin_unlock(&amp;spin); <span class="comment">/* 自旋锁解锁 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line">		usleep(<span class="number">1000</span>);</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	pthread_exit(<span class="string">&quot;threadMutex2 exit!&quot;</span>);</span><br><span class="line"></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure><p>程序中的宏<code>macro_spin</code>用于决定是否使用自旋锁。</p><ul><li>若<code>macro_spin</code>为<code>0</code>，则不使用自旋锁。</li><li>若<code>macro_spin</code>为<code>1</code>，则使用自旋锁。</li></ul><div class="tabs" id="tabname2"><ul class="nav-tabs"><li class="tab active"><a href="#tabname2-1">macro_spin == 0</a></li><li class="tab"><a href="#tabname2-2">macro_spin == 1</a></li></ul><div class="tab-content"><div class="tab-pane active" id="tabname2-1"><p>在终端执行以下命令编译程序：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall -l pthread # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure><p>然后，终端会有以下信息显示：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">This is threadMutex1 thread create,ret=0,tid1=140129428600384</span><br><span class="line">This is a threadMutex1 thread!</span><br><span class="line">This is threadMutex2 thread create,ret=0,tid2=140129420207680</span><br><span class="line">This is a threadMutex2 test!</span><br></pre></td></tr></table></figure><p>然后我们打开<code>test.txt</code>文件，查看文件内容如下：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">II  wrwriittee  tthhrreeaaddMutMuext2ex l1 inlei</span><br><span class="line">ne</span><br><span class="line">I wIr iwtre itteh rtheraedaMduMtuetxe2x 1l ilnien</span><br><span class="line">e</span><br><span class="line">I Iwr iwrtiete  tthhrreaeaddMuMutteexx21 l liinnee</span><br><span class="line"><span class="meta prompt_"># </span><span class="language-bash">后边的省略 ......</span></span><br></pre></td></tr></table></figure><p>该文件被两个线程共享，两个线程都是写入，未保护共享文件，导致文件写入出错。</p></div><div class="tab-pane" id="tabname2-2"><p>在终端执行以下命令编译程序：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall -l pthread # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure><p>然后，终端会有以下信息显示：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">This is threadMutex1 thread create,ret=0,tid1=140667718608448</span><br><span class="line">This is a threadMutex1 thread!</span><br><span class="line">This is threadMutex2 thread create,ret=0,tid2=140667710215744</span><br><span class="line">This is a threadMutex2 test!</span><br></pre></td></tr></table></figure><p>然后我们打开<code>test.txt</code>文件，查看文件内容如下：</p><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">I write threadMutex1 line</span><br><span class="line">I write threadMutex2 line</span><br><span class="line">I write threadMutex1 line</span><br><span class="line">I write threadMutex2 line</span><br><span class="line"><span class="meta prompt_"># </span><span class="language-bash">后边的省略 ......</span></span><br></pre></td></tr></table></figure><p>该文件被两个线程共享，两个线程都是写入，使用自旋锁保护共享文件，文件写入正常。</p></div></div></div>
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    <p><span>文章标题:</span><a href="/post/9629078.html">LV05-03-线程同步-03-自旋锁</a></p>
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